Work vehicles can be equipped with booms for doing excavation, harvesting, logging and other heavy-duty work. In FIG. 1, for example, a work vehicle 100 such as a tracked harvester is shown. The vehicle 100 includes an undercarriage 102 to which a ground engaging assembly 104 is provided for supporting and propelling the vehicle 100. The ground engaging assembly 104 can include tracks, as shown, or alternatively may include tires. The vehicle 100 is provided with a supporting structure 106 which is disposed upon the undercarriage 102. A cab 108 is disposed adjacent to the support structure 106 and can include control levers, joysticks, and other assemblies for controlling the movement and operation of the vehicle 100.
The work vehicle can also include a work attachment 110, such as a single grip harvesting head, for performing a working operation (e.g., logging). The work attachment 110 is pivotally mounted to one end of a dipper stick 112 which in turn is pivotally mounted to a boom 116. A first hydraulic cylinder (not shown) is used for pivoting the work attachment 110 relative to the dipper stick 112. Similarly, a second hydraulic cylinder 114 is provided for pivoting the dipper stick 112 relative to the boom 116 and a third hydraulic cylinder 118 is provided for pivoting the boom 116 relative to the supporting structure 106. The supporting structure 106 can be pivoted relative to the undercarriage 102 by a hydraulic motor (not shown). Although the work vehicle 100 is described for use as a tracked harvester, the embodiments of the present disclosure are not limited to the tracked harvester and may be incorporated in other work vehicles including a tracked feller buncher, wheeled feller buncher, etc.
The boom 116 is an elongated body that is loaded at both ends thereof during operation and is also heavily loaded at cylinder attachment points. Conventional booms are formed by materials having different thicknesses which are welded together. The boom structure is designed to achieve a desirable strength and service (fatigue) life, but also maintain a desirable weight that allows the hydraulic cylinder to operably control the boom. If a boom weighs too much, for example, the hydraulic cylinder can have difficulty controlling the boom during operation.
To achieve a desired strength and weight, a conventional boom will include side members having a thicker portion near each end and a thinner portion therebetween. One such example is illustrated in FIG. 2. A boom 200, similar to the boom 122 of FIG. 1, is shown having a first end 202 and a second end 204. For instance, the first end 202 of the boom 200 can be pivotally coupled to one end of a dipper and the second end 204 can be pivotally coupled to a support structure. The boom 200 also includes a set of cylinder lugs 212 near the middle for coupling to a hydraulic cylinder. The structural design of the boom 200 includes a top member 214, a pair of side members 206, and a bottom member 220. Each of the side members 206 is formed by a first, thicker body 210 disposed near the first end 202 and second end 204 and a second, thinner body 208 disposed in between. The thinner body 208 can have a thickness of about 10-20 mm and the thicker bodies 210 can have a thickness of about 40-50 mm. The thicker bodies 210 and thinner body 208 are welded together to form the side member 206. Likewise, the side members 206 are welded to the top member 214 and bottom member 220.
There are several shortcomings found in the structural design of the conventional boom 200. First, the interfaces 216, 218 between the thicker bodies 210 and thinner body 208 can form significant stress risers which reduce the strength of the boom 200. The stress risers can eventually cause cracks near each interface 216, 218. In addition, the thinner body 208 is susceptible of being dented or damaged during boom operation and therefore weakening the boom structure, particularly since the thinner body 208 is welded directly to the top member 214, bottom member 220, and each thicker body 210.
Another shortcoming of the conventional boom structure is the required use of a weld support or backup bar. Referring to FIG. 3, an example of a weld support bar 300 is shown. In this illustration, the top member 214 is removed so that the weld support bar 300 is visible. The weld support bar 300 comprises a series of individual, elongated bars or rods of material welded at the interface of the top member 214 and side members 206. The size and shape of these support bars 300 can be difficult to weld and do not form a continuous, uniform weld backup. Cracking or other failures can occur at locations where there is a discontinuity or interruption between adjacently welded support bars 300 (i.e., along the length of the boom). Further, the weld interface between the top member 214 and side members 206 formed a fillet weld, which provides less strength and support to the boom compared to a penetration weld.
A need therefore exists to provide a boom having a structural design that possesses an increased strength, without increasing the weight of the boom, and includes a continuous weld backup.